My Devil's Heart
by Brunetta6
Summary: A One Piece-Frozen Crossover AU for Panda-san. Kuzan and Sakazuki have never been the best of siblings. But when the elder prince's icy abilities run amok and he flees from his extremist younger brother, inherited wills, a weirdo with a reindeer, and an impending apocalypse come to play… and it might just be more than any one man can handle alone. Even a man with a Devil's Heart.


**This fic is rated T for violence and some bad language. There have been One Piece OSTs added, the storyline, twists, and pacing of the movie as well as the lyrics from the Frozen OSTs have been changed, and some mood music primarily from Two Steps from Hell. *FLAILS* YOU HAVE NO IDEA how many feels I have had in development of this storyline! As a HUGE FAN of the manga/anime and an affectionate critic of the movie… although this is my first attempt at a crossover EVER, I must say this will be an ****amazing**** experience for us all.**

**Altered song in the context is based off the Frozen OST "****Frozen Heart****."**

**Enjoy.**

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– _**Prologue**_** –**

**The Devil's Heart**

"_Born of cold and burning air  
__And false sunlight combining!  
__This curséd force both foul and fair  
__Is the Devil's Heart a-beating…_

_So cut through the heart, cold and clear.  
__Strike for love or strike for fear.  
__See death, for there is danger here.  
__Split all three apart…  
__And break the Devil's heart!_

_Bending light! Killing snows!  
__Falling flame! Never slows!_

_Beautiful!_

_Powerful!_

_Dangerous!_

_Dark._

_The maelstrom has power, it can't be controlled!  
__Stronger than one, stronger than ten  
__Stronger than a hundred men! _

_Born of cold and burning air  
__And false sunlight combining!  
__This curséd storm both foul and fair  
__Is the Devil's Heart a-beating…_

_Cut through the heart, cold and clear!  
__Strike for love or strike for fear!  
__There's death and there is danger here!  
__Split all three apart…_

**_Beware the Devil's Heart."_**

So was the lore of the paradise kingdom Marie Jois.

In the ancient mythology of the Red Line Islands, a prophecy spoke of three fruits – one with the power of ice, another of magma, and another of light. If they were eaten, individually, the people who wielded these powers would be unstoppable, invincible forces of nature. But together, they would become the Devil's Heart… a storm that was only described in the ancient writings as the apocalypse itself. No one knew when the three Devil Fruits would come forward, which island they would come from, or how they would even come into being. But as time passed, the people of Marie Jois lost their belief in their wielders and the storm that would destroy the world.

Little did they know, the threat of an apocalypse was still very real. And 800 years later, the first of the Devil's Hearts appeared in a place no one was expecting. Least of all the poor boy himself.

And that boy was…

**.oOo.**

"KUZAN!"

"OOF!"

Kuzan – the nine-year-old, eldest prince of Marie Jois – was rudely awakened by the missile of a ballistic little brother jumping on his stomach. He shoved his sibling off the bed. "YOU LITTLE TURD, ZUKI, GET OFF!" he yelled, delivering a punch to his head for good measure and snuggling back into his warm cocoon of blankets.

Eight-year old Sakazuki hit the ground with an undignified _splat_.

He sprung back up without even missing a beat. "GET YOUR BUTT OUTTA BED!" he insisted, pulling on his big brother's frazzled mop of black hair until Kuzan roared and sat up. "IT'S SNOWING!"

Sakazuki's face hit the floor again. _Splat._

"Then go freeze by yourself!" Kuzan snapped.

He flopped back onto his pillow, eyes snapping shut again. "I wanna sleep."

On the floor, the younger boy sat up – pouting at his dilemma… then, all at once, he perked up. Giggling mischievously, little Zuki flipped up the covers and crawled under Kuzan's bed; a couple seconds later, his eyes poked over the edge of the mattress, peering at his older brother's sleeping face.

"Come _on_!" he smirked. "Let's build a _snow fort_."

For a second, the older boy gave no sign of hearing.

Then… one eye slowly opened.

A few minutes later, Kuzan and Zuki were bursting out the front door of the castle – still trailing the poor servants who had been charged with bundling them up.

"My young princes, don't – just – UGH!" one of the young men huffed.

He gave up trying to wrap a scarf around the struggling Kuzan, threw up his hands in surrender, and walked back into the castle, passing the queen of Marie Jois on her way to the door.

The beautiful, brown-haired queen blew into her hands to ward off the temperature and rubbed her velvet-clad shoulders; she leaned against the stone threshold, smiling as she watched her boys tumble around in the snow-blanketed courtyard. Although Marie Jois was usually a sunny paradise of white marble, tropical plants, and shining fountains, the erratic weather of another nearby island chain – the Grand Line – often drifted into the Red Line, making heat waves in the dead of winter or freak midsummer snowstorms like this one relatively normal. Now, tall palm trees rustled in a gentle, ice-scented wind. The gardens of frozen tropical flowers clinked like crystal against one another. The sky was pale, pristine, and very, very bright. Privately, the queen shielded her eyes. "I wonder if they can even see out there…" she worried.

"I wanna play _toooooo_!" came a youthful, drawling voice.

A skinny kid with a hooked nose, squinty eyes, and lips permanently fixed in a kissing pout ran out into the courtyard, kicking up snow in nothing but his pajama shirt and underwear. The queen raised an eyebrow concernedly at her nephew's state of dress, but didn't have time to say anything.

Instead, she just smiled. "Oh dear, cousin Borsalino, too?" she chuckled, rubbing her shoulders again to ward off the chill.

"That boy always shows up in the strangest places…" her husband replied.

King Sengoku came to join his queen at the door, folding his thick arms as they watched their sons complain at their annoying cousin. He was a powerfully built man, with an impressive head of hair, neat mustache, and long black goatee, neatly tied into a single braid down his chest. Kuzan and Sakazuki were definitely their parents' children; had inherited the best features of both monarchs; the king's black hair – so curly it bordered on being an afro – with his mother's dark, heavy-lidded eyes, long face, soft mouth, and deep brown skin. Sakazuki, on the other hand, was a clone of Sengoku – the same narrow eyes, wide mouth, and stern, scowling countenance – but for the queen's straight, light brown hair. Sengoku supposed his wife had to have been a right rascal when she was young; he couldn't attribute their mischievous streaks to himself no matter how he looked at it; Zuki threw a snowball, Borsalino threw five back, Kuzan got caught in the crossfire – screaming in revulsion when he discovered a _bit _too late that a sphere that had landed in his mouth had gravel and something mushy in it – and soon it was an all-out war between the three little boys.

Each darted to an edge of the courtyard and hastened to build their snow forts as the king and queen of Marie Jois looked on. "The other day I found him in the royal library, which wouldn't be surprising, but it was in a section only our scholars have the keys to!" Sengoku marveled.

He sighed in relief. "We're lucky he's only staying for the summer. Otherwise he might find his way into the treasury and spend all our money on candy."

"Oh, that would never happen!" his wife laughed.

Meanwhile, Zuki had spotted an opening when Kuzan ducked to grab more snowballs. Not pausing to think about what he was going to do once he got there, the boy made a dash to the enemy fort – dodging through heavy fire from Borsalino – and blindsided his brother. "FOR MARIE JOIS!" he crowed.

Kuzan landed facedown in the snow. "OOF! ZUKI!" the dark-haired boy yelled in complaint. Blowing ice flakes out of his nose, he bucked his little brother off his back.

Zuki took flight – straight into a drift. "WAH!"

His yelp was abruptly cut off by a _poof_ of snow. Kuzan leapt after him, both boys colliding in a flurry of insults, runny noses, and little fists chapped by the cold. They were always like this; if you asked one whether he loved the other, he would make gagging noises and say no, he hated that jerk! And they'd probably pick another fistfight just to prove you wrong. Therefore – despite being told they should behave better as princes – they were forever adding to each other's collection of bumps and bruises. They were little brutes, they were. But they were boys and brothers. Too much alike to stay apart for long.

"OWWWW, LEGGO MY HAIR!"

"STOP BITING ME, THEN!"

But something was about to happen…

"I MEAN IT!"

That would change their family…

"LET –!"

Their lives…

"ME –!"

And their hearts _forever_.

"**GO**!"

Kuzan's fist caught his little brother under the eye.

A concussive blast of freezing wind ripped across the courtyard. King Sengoku grunted in surprise and reacted, grabbing his queen without thinking to shield her from the wind; the gale tore at their clothes and hair, screaming through and around the castle corridors like the waking shriek of a horrible, winged beast. Borsalino was hurled bodily through the air, smacked against the courtyard wall, and slid to the ground.

He shook his head in amazement. "_Wowwww_!"

His fort buried him completely. _Splat._

Then…

Almost as if in slow motion, Zuki fell over – and gently hit the ground. The sound his body made in the snow was deafening in the deadly silence.

…_Crunch._

Kuzan sat up, grouchily brushing himself off – completely oblivious to the blast that had just flattened the entire garden. "Hmph!" he grouched, glaring at his brother face-down in the snow. "Serves you right, you little turd."

He was expecting Zuki to shoot back some kind of insult and fly at him again…

But he wasn't moving.

Kuzan blinked.

He coughed and laughed nervously. "Hey, you jerk, quit playing around! I know you're faking!"

Zuki didn't move so much as a finger.

Panic rose in the nine-year old's throat as he poked his little brother… then began to shake him violently, his voice rising in pitch until he was almost screaming. "Zuki? Zuki! This isn't funny! ZUKI! GET UP!"

Kuzan's streaming eyes focused on his parents, who were still huddled in the open doorway of the castle – pale with shock. "MAMA, PAPA!" he sobbed.

Suddenly, the young prince gasped as ice shot from his chapped little hands, crackling over Zuki's body like a thick crystal blanket. Frightened, Kuzan reeled back from the sharp noise and landed on his rear end in the snow; although the ice halted its path over his brother, the snow around him began to freeze solid. A vortex of snow began to spin, adding to the pile, trapping his arms and legs as it crawled higher and higher up his neck –!

"PAPA!" Kuzan wailed, tears freezing so fast they blinded him. He couldn't close his eyes! He couldn't move, he couldn't _breathe_ –!

"_**PAPA**_!"

The last thing he saw before he blacked out was his father rushing towards him.

King Sengoku burst through the vortex of ice like a tank, one powerful hand fastening onto his boy just as the snow covered his curly black head. And with a mighty roar, he _ripped_ Kuzan free. Ice shattered and broke. Glittering splinters flew through the air, throwing rainbows in every direction – beauty that only made the direness of the situation more apparent. Sengoku clasped his son to his chest. Eyes wide, he raked the hair away from the boy's unconscious face, desperately searching Kuzan for any sign of injury. He didn't feel the chill. The king's dark eyes flickered between Kuzan and Sakazuki. He only felt confusion, and _worry_, and what in the _world_ had just –?!

Then, suddenly, it hit him.

Dread made Sengoku's blood run cold – not the tendrils of frost that began to creep up his fingers. Eight hundred year old lore came rushing back, read in a dull book in an equally dull history lesson. A prophecy.

The Devil's Heart.

The king gazed down at his son with new eyes. The ice was encasing Kuzan's body now, tiny spikes digging into Sengoku's chest – almost protectively, angrily, like it was threatening him with a wrath of its own.

His heart caught in his throat. _Oh please, god, no…!_

Behind him, his queen ran to Sakazuki. She plucked their younger son from the snow; her dark eyes contracted in fear. "He's ice cold!" she breathed.

She looked to Sengoku.

The king hesitated.

Then, he took a deep breath. In… and out… and then, he opened his eyes determinedly. "I know where we need to go."

** .**

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**A/N: To give the prologue time for exposure, Chapter 1 – the life of our dear Zuki and Kuzan before the REAL story begins – will be up in a few days. See you then!**


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